Sandra Díaz and Yadvinder Malhi published an interesting and broad review of the biodiversity literature, that this forum might be interested in. https://www.annualreviews.org/doi/pdf/10.1146/annurev-environ-120120-054300
Some interesting tables and figures from the academic paper:
For those that might feel daunted at the paper’s length or complexity, here are the summary points and future issues from the conclusion:
SUMMARY POINTS
- Since its origin in the 1980s, the concept and use of the term biodiversity have evolved
quickly and now have multiple dimensions.- Biodiversity has multiple values ranging across intrinsic, instrumental, and relational values, which differ strongly among social actors.Which of these values predominate or are
even considered has a major influence on practical decisions about biodiversity.- Approximately 2 million species of living organisms are currently described; the total number of species on Earth is estimated, with much uncertainty, to be 10 million.
Species-level diversity is dominated by terrestrial animals (especially arthropods), but
marine and microbial systems contain a particularly rich phylogenetic diversity.- Humans have affected global biodiversity since prehistoric times both negatively (e.g.,
megafaunal and island extinctions) and positively (e.g., stewardship of organisms and
ecosystems, creation of new ecosystems).- The reconfiguring of life on Earth at all levels, from genes to biomes, by humans is now
evident. The rate of decline of biodiversity has intensified in modern times. Current
extinction rates are much higher than prehuman ones. The extent and integrity of natural
ecosystems; the functional, phylogenetic, and species-rich distinctiveness of local biotas across the > world; the size of wild plant and animal populations; and the intraspecific genetic diversity of wild and domesticated organisms have all decreased.- The primary direct drivers of modern biodiversity decline include changes in the use of
land, freshwater, and the oceans; increased harvesting of wild organisms; climate change;
various forms of pollution; and invasive species. To date, climate change is a relatively
minor cause of biodiversity decline but its impact is likely to rise greatly over this century.
These drivers interact in complex ways, sometimes ameliorating and often reinforcing
each other’s effects.- The indirect drivers of biodiversity decline are increasing. Prominent among them are
globally telecoupled consumption footprints, concentrated in certain countries and societal groups. Indirect drivers affect the rate and magnitude of preexisting direct drivers
and give rise to new ones, such as plastic pollution, noise and light pollution, and seabed
exploration and exploitation.- Addressing these underlying drivers requires bold system-wide rethinking and reorganization to put biodiversity at the center of societal values, planning, and goals.
FUTURE ISSUES
- Several emerging or neglected drivers of biodiversity decline warrant particular attention and study. These include plastic pollution, noise and light pollution, and seabed
exploration and exploitation.- We need to better understand the biodiversity of novel ecosystems being created by biotic homogenization and climate change and to better contextualize the trade-offs and
tensions between place-based biodiversity values (e.g., native species) and functional values (e.g., resilience of whole ecosystems over levels of species diversity).- The multiple values of biodiversity, and its multiple valuers, including local traditional
and Indigenous communities, need to be better incorporated into global framings of
biodiversity.- Many frontiers of biodiversity, including tropical forest canopies, species-specific mutualists or parasites, gut microbiomes, the seafloor and soil sediments, and deep biosphere
microbial communities, are still poorly explored.- We need a more refined understanding of how different components in the fabric of
life interact with planetary function, such as maintenance of resilience to extreme events
and climate change, as well as underpinning finer-scale contributions to different people
across the world.- We need to better understand how to fully embed biodiversity into societal values, policy planning, and decision-making to enable the systemic shift required to reverse the
ongoing decline.
Thanks. Interesting. I’ll have a read. It reminds me of a great graphic I came across recently that uses the same data as this paper uses for it’s Figure 1, to visualize the total global biomass of the different types of life on Earth. https://www.visualcapitalist.com/all-the-biomass-of-earth-in-one-graphic/
Thanks for sharing figures and summaries of this paper, Matt!
Honestly, those numbers look far, far too low to me.
There are approximately 103,000 species of wasp alone known (and more of Hymenoptera), which according to the numbers in this paper would mean that wasps, just by themselves, account for close to 10% of all arthropods.
Coleoptera has some 400,000 identified and described species so far, with total species estimates ranging from 0.9-2.1 million species, again, just of Coleoptera. That means that Coleoptera, by themselves are potentially greater in number than what this paper proposes as the total number of species of the phylum Coleoptera falls within. Obviously that doesn’t work.
The range of estimates for animalia alone on Earth is all over the place, often hovering around 10 million as a low end semi-consensus, but ranging up to over 30 million or more species depending on who is doing the estimate and what methods they’re using.
In short, total species estimates are still in a very uncertain state, with estimates already higher than the numbers given in this paper, and and with so many cryptic species being revealed by genetic analysis the actual number is likely to be vastly higher than even generous current estimates.
From the paper:
4.1. How Much Biodiversity Is There?
…Note that these figures refer to species already described; there is high uncertainty about how
many species there are in total. The most widely cited assessment uses the relationship between
taxonomic level and species diversity of better-understood taxonomic groups to infer species
counts for more poorly understood groups (34) (Figure 1; Table 2). This approach suggests
8.7 million eukaryotic species (±1.3 million). Approximately 8.1 million of these are plants and
animals, of which approximately 5.5 million are insects (34, 35). We are nowhere near describing all species on Earth: According to the same assessment (34), and assuming that the average effort
and cost to describe an animal species remain constant (this could change dramatically with
new technology, for example), it would take approximately 1,200 years and the effort of 303,000
taxonomists to describe all eukaryotic species on the planet. Recent estimates (36) employing
molecular-based species delimitation (rather than the usual morphology-based delimitation) of
arthropod species boundaries controversially suggest that eukaryotic diversity may still be much
higher (approaching 1 billion species in total).
Which reinforces my initial comment, and makes the numbers presented in the tables in the paper pretty much irrelevant.
Given that there is no agreed-upon number of base pairs that defines a difference between species, most of these cryptospecies are hypothetical. Now, if the genetic analysis is corroborated by demonstrable reproductive isolation, allopatry, or niche partitioning, that would lend support to the cryptospecies being real entities.
An arbitrary amount of genetic difference is not what is used to define a species in any event. Some distinct species are very close genetically, and some single species have a very large amount of genetic variability within the population.
Delimiating markers between species (or between subspecies) is a complicated thing, and there is a lot that goes into it, with no single metric being the be-all-and-end-all factor.
Certainly there are a lot of hypothetical species, but I’m talking about ones that have been revealed and confirmed.
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